linux-kernel - Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel

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Message-ID: <m1r68shjhb.fsf@frodo.ebiederm.org>
Date:	Wed, 13 Aug 2008 11:12:48 -0700
From:	ebiederm@...ssion.com (Eric W. Biederman)
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Huang Ying <ying.huang@...el.com>, Pavel Machek <pavel@....cz>,
	nigel@...el.suspend2.net, "Rafael J. Wysocki" <rjw@...k.pl>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Vivek Goyal <vgoyal@...hat.com>, mingo@...e.hu,
	linux-kernel@...r.kernel.org,
	Kexec Mailing List <kexec@...ts.infradead.org>
Subject: Re: [PATCH] kexec jump: fix compiling warning on xchg(&kexec_lock, 0) in kernel_kexec()

Linus Torvalds <torvalds@...ux-foundation.org> writes:

> On Wed, 13 Aug 2008, Huang Ying wrote:
>>
>> -	xchg(&kexec_lock, 0);
>> +	locked = xchg(&kexec_lock, 0);
>> +	BUG_ON(!locked);
>
> Why do you want to do this at all? 
>
> And why do you implement your locks with xchg() in the first place? That's 
> total and utter crap.
>
> Hint: we have _real_ locking primitives in the kernel.

This part certainly.

The way the code should work, and the way it has in the past is:
image = xchg(&kexec_image, NULL)
if (!image)
   return -EINVAL;

Very simple and very obvious and very easy to get right, and it has
been that way for years.

Eric
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